Talreja, Kavita; (1996) Stress induced changes at the yeast plasma membrane. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

In most organisms a mild sub-lethal stress increases the capacity for survival during a subsequent lethal stress. The mechanisms that implement this acquisition of tolerance have been subject to numerous studies. Best characterised is the induction of heat shock proteins (hsps) at elevated temperatures. Very little is known about heat shock associated events occurring at the plasma membrane. This is surprising bearing in mind that the first component of the cell to encounter certain types of environmental stress may be the cell envelope. Work described in this thesis has identified several changes to yeast plasma membrane proteins with ethanol stress and weak acid stress. Two prominent changes to the protein composition of the S. cerevisiae plasma membrane were seen with 6% and 8% ethanol stress; (i) a marked decrease in levels of the H+-ATPase and (ii) the acquisition of hsp30. These are the same two changes that result from a sub-lethal heat shock. Weak acid stress was found to induce a protein of approx. 150kDa at the plasma membrane in both S. cerevisiae and Z. bailii. Protein sequencing identified this protein in S. cerevisiae as the product of the SNQ2 gene. Pulse labelling studies have shown this protein to be specifically induced by sorbic acid and not appreciably glycosylated. Salt and heat stress were found to induce this protein at the level of transcription but it is not seen by SDS-PAGE analysis of purified plasma membranes from cells exposed to these stresses. A mutant disrupted in the HSP30 gene was generated in a protease deficient genetic background and used in comparative physiological studies with the wild type parent in order to establish a phenotype for loss of the heat shock protein. Thermotolerance and membrane permeability studies were carried out with the wild type and hsp30 strains but no significant difference between these strains was apparent. However the hsp30 mutant took longer to adapt to growth in the presence of sorbic acid

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